I started using a Take-A-Look mirror a few years ago. I like it so much that I carry it with me when I don't ride, in case I grab a bike unexpectedly. Since I've been using it, my skill with it has increased. I can now sweep and take a look, and I feel that I can see around myself in almost 360º. I like being able to merge left more quickly and confidently.

If you're just starting with a mirror, don't be too confident. Look with the mirror and then turn your head to confirm. The first time I used one, I looked, didn't see a car, and then moved and discovered there was a car there. I didn't get hurt, but it was scary.